The Institute of Medicine and the American College of Emergency Physicians have identified emergency department (ED) crowding as a critical threat to public safety. Exposure to dangerously crowded ED conditions is associated with a 30-80% relative risk increase in short-term mortality and results in decreased timeliness of care, lower patient satisfaction, and disparities in healthcare access. However, effective strategies to reduce ED crowding remain ill-defined despite a decade of operations research. The long term-goal of our research program is to eliminate patient harms associated with ED crowding. To address the limitations of the existing literature, we propose a hypothesis-generating study to identify, classify, and measure hospital practices to reduce ED crowding. Our qualitative research plan will study natural experiments at hospitals with varying levels of performance. This project will be performed in partnership with the ED Benchmarking Alliance (EDBA), which is a unique collaborative of over 800 hospitals that collects standardized ED crowding data. This proposal will create the tools to perform a national comparative-effectiveness study of hospital practices to reduce ED crowding. We will achieve the following Specific Aims: Aim 1. Identify hospital practices directed at reducing emergency department crowding. Aim 2. Develop a reliable and valid survey to measure hospital practices directed at reducing emergency department crowding. Subsequent research will combine originally collected survey data from a national random sample of hospitals with public reports of performance on ED crowding measures (released by Medicare in early 2013)~ quantitative analyses will assess the impact of different hospital practices on ED crowding and patient relevant outcomes such as mortality and satisfaction. Our long-term research plan has high potential to change the organizational standard-of-care and to eliminate patient harms caused by ED crowding.